EVOLUTION OF COLORADO'S FRONT RANGE DURING THE LARAMIDE OROGENY

During the Laramide Orogeny, the Colorado Front Range segment of the Rocky Mountains developed over 6400 meters of structural relief. This uplift took place primarily along north-south oriented thrust faults. Foreland basins filled with synorogenic sediments on the eastern and western flanks of the range. On the eastern side of the range, the uplift took place in two pulses. Synorogenic strata in the Denver Basin reflect both episodicity of sedimentation and the development of distinct environmental gradients associated with the establishment of local topographic relief. On the western side of the range, sedimentation in the South Park Basin may have been more continuous, although the record is less well understood.

Variations in the composition of the synorogenic strata on both sides of the Front Range reflect significant changes in the character of the materials eroded from the growing mountains. Clastic materials are dominated alternately by arkosic and andesitic debris. Unroofing histories can be documented, as well as an episode of widespread extrusive volcanism. Through interpretation of dated successions of synorogenic sediments in both basins, a series of paleogeographic models have been prepared that schematically illustrate these changes in source area rock exposures through time.

These models can be combined with paleontological observations to develop paleo-ecological reconstructions of high fidelity. Better understanding of ecosystem evolution through time will aid in interpreting the significance of faunal and floral dispersal patterns in the Rocky Mountain region during the Laramide Orogeny.